DMA repair and damage tolerance processes are absolutely critical to preserving human health following exposure to many different agents. The long term goal of this research is to develop a detailed integrated understanding of the molecular mechanisms responsible for environmental mutagenesis in eukaryotes. In molecular processes that are both complex and elaborately controlled, mutations are introduced when specialized translesion synthesis (TLS) DNA polymerases copy over DNA damage caused by environmental agents. The proposed research places a special emphasis on Rev1, which by virtue of acting both as a scaffold for other TLS DNA polymerases and as a polymerase itself, lies at the root of eukaryotic mutagenesis. We will follow up on our unanticipated finding that S. cerevisiae Rev1 is expressed 50 fold higher during G2/M than in G1 and most of S phase by investigating the basis of its cell cycle control," which is predominantly posttranscriptional;promising candidate regulatory genes such as UMP1 and CDC7 will be tested, genetic screens for new regulatory genes will be carried out, and experiments will be conducted to determine the importance Of this control: Using both biochemical and genetic approaches, we will continue to investigate the structural and functional basis of Rev1 interactions, focusing particularly on the interactions of the Rev1 C-terminal domain, its BRCT domain, and its ubiquitin-binding motifs. We will investigate the functional importance of the Rev1 polymerase activity by following up on our recent observations suggesting that Rev1 may have a class of cognate lesions it replicates particularly well. We will investigate the function and regulation of S. pombe DinB and its relationship to Rev1. We will develop a high-throughput assay, based on disruption of the Rev1-Rev7 interaction, that will allow screening for inhibitors of eukaryotic environmental mutagenesis. The proposed research will make a highly significant contribution to basic science by elucidating the still poorly understood eukaryotic translesion synthesis mechanisms responsible for most mutations. These mutations contribute to aging, cancer, and various human diseases. Identification of additional genes that play roles in these mutagenic processes will help make it possible to address the question of why only some people develop disease when exposed to an environmental toxin. Small molecule inhibitors of TLS could lead to novel "anti-mutagenesis" drugs with multiple applications to human health.